The present invention is related to systems for removing volatile organic compounds from effluents and, more particularly, to systems for removing volatile organic compounds from the effluents of a semiconductor fabrication facility.
Many processes used in the fabrication of semiconductor devices require subsequent cleaning steps with organic solvents or the use of an alcohol to dry the device by removing water and producing a hydrophobic surface. Removal of these organic compounds from a semiconductor wafer surface usually requires directing a gas, such as nitrogen, to flow across the wafer surface. The resulting effluent gas stream is laden with volatile organic compounds (hereafter termed VOCs). If released into the atmosphere, these volatile organic compounds can react with sunlight to produce photochemical smog or can cause other environmentally detrimental effects.
As a result, environmental regulations strictly limit the amount of VOCs which may be released into the air. It is desirable, then, to remove a high percentage of these VOCs prior to releasing these effluent gas streams into the air. It is further desirable that a VOC removal system be flexible in operation to allow a wide range of inlet gas of flow rates and VOC concentrations, so the cleaning or drying processes are not impaired nor compromised.
A previous VOC removal technique has been the use of an absorption medium, such as activated carbon, to remove the VOCs. However, this technique has the disadvantage of creating a solid waste product which must then be disposed of at substantial cost.
A better approach is to remove the VOC vapor by condensation. It is much more desirable because the resulting liquid may be recycled at much lower cost. However, the problem in most condensation systems is the formation of fog, which consists of very tiny droplets of the VOC. Such tiny droplets do not settle out of gas streams, but remain suspended within it. The fog droplets also flow with moving air streams and avoid contact with solid surfaces. As a result, the removal of fog droplets is notoriously difficult. Fog forms when a gas stream is cooled below the dew point of its condensable vapor constituents. Fog formation is common when a gas stream containing condensable vapors is cooled in a condensing unit with a low surface area-to-volume ratio.
On the other hand, the present invention provides for a volatile organic compound removal system which has an extremely high surface area to volume ratio. The system also has good thermal conductivity to assure that the surfaces are cooled appropriately to condense the VOCs.
The present invention provides for a compact, volatile organic compound removal system. The system comprises a metal condensation plate and a cooling source in intimate thermal contact with the metal condensation plate. The metal condensation plate has a channel formed in the plate, an inlet in the condensation plate for introducing a gas carrying volatile organic compound vapors into the channel, a high surface area metallic structure in intimate contact with the walls of the channel, an outlet in the condensation plate for removing the gas from the channel and a drain in the condensation plate for removing volatile organic compound condensates from the channel. The cooling source cools the channel walls and the high surface area metallic structure so that the volatile organic compound vapors condense on the high surface area metallic structure to be removed from the gas. Foamed metal works effectively as the high surface area metallic structure. Alternatively, metal fins can also work as the high surface area metallic structure.